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The airflow in cubic metres per hour, as printed on the datasheet.
Check which row the figure came from. Manufacturers publish free-delivery airflow alongside airflow at a stated external static pressure, and on a compact heat recovery unit the two can be a long way apart. Convert the figure quoted at the pressure your ductwork will actually impose, not the headline one.
Airflow
500.3 CFM
Converted using an exact defined factor of 0.5885777786914765 CFM per m³/h. Exact to the digits shown, but volume flow and mass flow are different things: at altitude or in hot air the same m³/h carries less air, so heat transfer still needs a density correction.
- Conversion factor applied
- 0.59 CFM per m³/h
They open the calculator with your figures already in it
Cubic Metres per Hour to CFM Calculator: 500 CFM — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- This is the reciprocal of 1.69901079552. Exactly, 1 m³/h = 97656250 / 165919023 CFM = 0.588577778691476…, a repeating decimal, so the multiplier here is that exact fraction rounded to 16 significant figures. The definition it derives from — 1 ft = 0.3048 m exactly — is exact; only its decimal form is not.
Inputs used
- Airflow (m³/h)
- 850
Intermediate steps
- Conversion factor applied
- 0.59 CFM per m³/h
Confidence note: Converted using an exact defined factor of 0.5885777786914765 CFM per m³/h. Exact to the digits shown, but volume flow and mass flow are different things: at altitude or in hot air the same m³/h carries less air, so heat transfer still needs a density correction.
What this calculation does not cover
- Dividing the converted CFM by a design velocity gives a free area, and a free area is not a duct size. Internal acoustic lining eats into the bore, flexible duct only reaches its rated diameter pulled taut and loses capacity fast once a run is left slack, and a rectangular duct squashed flat to clear a ceiling void carries less than a square one of the same area because the wetted perimeter grows against it. Build to the area this arithmetic gives you and the installed duct is tighter than the calculation assumed.
- The m³/h printed on the datasheet was measured with clean filters, and that assumption rides through the conversion untouched. On a constant-speed unit the airflow drops as the filters load, so a rate that just met its target on commissioning day sits under it for most of the interval before the next filter change — the figure worth converting is the flow at the dirty-filter resistance the manufacturer states, not the headline clean one.
Add the equipment this sizes
This result is a specification — 500.3 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- This is the reciprocal of 1.69901079552. Exactly, 1 m³/h = 97656250 / 165919023 CFM = 0.588577778691476…, a repeating decimal, so the multiplier here is that exact fraction rounded to 16 significant figures. The definition it derives from — 1 ft = 0.3048 m exactly — is exact; only its decimal form is not.
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Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
A schedule written in m³/h — a Continental air handling unit, an imported heat recovery ventilator, a car park extract designed abroad — has to become CFM before a North American duct sizer, a filter face velocity in FPM or a diffuser selection table can be used on it. This page is for the installer or detailer doing that translation with the equipment already on site. The trap unique to this direction is the ×0.6 habit: it runs 1.9% high, so a 5,000 m³/h duty is credited with 57 CFM it does not have, and the error leans optimistic on every branch at once. Dividing by 1.7 is closer, 0.06% low, but the exact factor costs nothing.